Internal and internal-external surface heat exchange tubing



C. H. KUTHE Nov. 17, 1959 INTERNAL AND INTERNAL-EXTERNAL SURFACE HEATEXCHANGE TUBING Filed July 16, 1956 FIGJ.

INVENTOR.

CHARLES H.KUTHE ATTORNEYS United States Patent INTERNAL ANDINTERNAL-EXTERNAL SURFACE HEAT EXCHANGE TUBING Charles H. Kuthe,Highland Park, Mich., assignor t 0 Calumet.& Hecla, Inc., Calumet,Mich., a corporation of Michigan Application July 16, 1956, Serial No.598,070

1 .Claim. .(Cl. 138-38) This invention relates :to .heat exchange tubingand refers more particularly tointernal andinternal-external surfaceheat exchange tubing.

The tubing in heat exchangeinstallations is often times provided with anexternal fin surface to increase the heat transfercharacteristics of thetubing. The construction of heat exchange tubing with an external finsurface is done primarily with prefabricated fins bonded mechanically ormetallurgically to a :smooth surfaced tube. Other finned tubing -.-isproduced with integral fins or corrugations on the external surface. Ithas been found, after much experimentation, that heat exchange tubingwhich is corrugated on the inside, either in addition to or in place ofexternal fins, greatly increases the heat transfer between theroutsideand inside fluids.

One object of this invention is to provide heat exchange tubing which iscorrugated on the internal surface so as to produce turbulence of thefluid within the tube and promote better heat transfer between theinside and outside fluids.

Another object of the invention is to provide a tube assemblycomprisingan outer tube and an inner tube positioned within the outer tube whichis corrugated on the innersurface.

Another-object of the invention is to provide a tube assembly comprisingan outer tube and an inner tube telescoped within theouter tube in heatexchange relation therewith, the inner tube being corrugated. to impartto the inner tube an undulating configuration in longitudinal section.

Still another object of the invention is to provide a heat exchange tubeassembly, as described in the preceding paragraph, in which the outertube has fins on its outer surface to cooperate with the inner tube inpromoting better heat transfer between inside and outside fluids.

Other objects are to provide a tube assembly as described in which theinner tube has a helical corrugation extending over a portion of itslength, and in which the inner tube has a plurality of longitudinallyspaced circumferentially extending corrugations.

Other objects of the invention will become more apparent as thefollowing description proceeds, especially when taken into considerationwith the accompanying drawings, wherein:

Figure 1 is an elevational view, partly in section, of a heat exchangetube assembly embodying the invention.

Figure 2 is a view similar to Figure 1, illustrating a modification.

Figure 3 illustrates a further modification.

Referring now more particularly to the drawing and especially to Figure1 thereof, the tube assembly there shown is generally indicated by thereference numeral and comprises an outer tube 12 and an inner tube 14telescoped within the outer tube in coaxial relationship therewith,these tubes being formed of a suitable material having good heattransfer characteristics. The tube=assembly 10 is-adapted to be employedin .a heatexchange;

installation.

The outer tube '12 is .cylindrical, that is, the radially inner andouter surfaces thereof areof uniform. circular cross-sectionthroughoutzthelengthof the tubeand, therefore, smooth.

outer surface of the tube to form a helical groove in the tube while atthe same time feeding .the tube-axially However, as pointed out: above,the

and rotating it. inner tube 14 maybe formed by other means.

The corrugated intermediate portion 20 has an un dulating configurationin longitudinal section as illustrated. The intermediate portion has ahelical radiallyinwardly extending corrugation 22, each convolution ofthe corrugation being indicated at 24. The undulating configuration alsoprovides, in effect, a helical radially outwardly extending corrugation26, each convolution of which is indicated at 28.

The crests 30of the convolutions 28'are'of the sameoutside diameter andare of the same diameter as the outside diameter of the cylindricalplain end portions 16- and 18. The crests 32 of the convolutions 24 areof the same inside diameter. It should also be pointed out that theinner tube 14 is of uniform wall thickness from one end to the other.

The tubes 12 and 14 are :assembled together by inserting the -inner tubewithin the outer tube and then-sinking the outer tube on the inner tube.or metallurgical contact of the two tubes is thereby achieved with thecrests 30 of the convolutions 28-of'the' inner tube contacting thesmoothinternal surface of the Preferably, the crests 30 have a full andcontinuous contact with :the smooth internal surfaceof Outer tube.

the .outer tube throughout the full .extentof the corrugated portion.Theexternal surfaces of the plain end portions- 16 and 18 are alsobrought into full and continuous surface-to-surface contact with thesmooth internal surface of the outer tube by the sinking operation.

As a result of this construction, a heat exchange tube assembly isprovided having a substantial helical corrugation on the inside andproducing turbulence in a fluid moving through the corrugated portion ofthe inner tube, and, hence, promoting better heat transfer with a fluidon the outer side of the tube assembly. The continuous and uninterruptedcontact between the crests 30 of the inner tube and the smooth innersurface of the outer tube also promotes heat transfer. The degree ofturbulence may be controlled by varying the shape of the convolutions ofthe corrugation on the inner tube.

Figure 2 illustrates a modification in which corresponding parts aredesignated by the same reference numerals. The inner tube 114 is exactlylike the inner tube 14 described in the first embodiment. The outer tube112 differs from the outer tube 12 previously described in that it hasan integral fin 115 formed on the external surface, the fin extendinghelically and continuously about the outer surface of the tube. Thecrests of the corrugations on the inner tube have a continuous anduninterrupted contact with the smooth inner cylindrical surface of theouter tube 112, thus achieving a mechanical or metallurgical contactbetween the tubes which may be accomplished in any suitable manner.

The fin 115 is shown as being formed integrally on Patented :Nov- 1 11.59

A mechanical at the outer tube although it will be understood that thefin may be prefabricated and bonded mechanically or metallurgically tothe outer surface of a smooth cylindrical tube such as the tube 12.

By varying height and linear spacing of the convolutions of the fin onthe outer tube, and also by varying the shape of the corrugation on theinner tube, the desired inside-outside surface ratio may be obtained foroptimum heat transfer.

.Figure 3 illustrates a further modification in which correspondingparts are designed by the same reference numerals. The outer tube 212 isexactly like the outer tube 112. The inner tube 214 differs from theinner tubes 14 and 114 only in the shape of the corrugated portion 220.The corrugated portion 220 is formed of a plurality of circumferentiallyextending longitudinally spaced radially inward corrugations 224 whichare disposed in a plane at right angles to the tube axis. Thecorrugations 224 are similar to the convolutions 24 shown in theprevious embodiments except that whereas the convolution-s 24 extendhelically and connect end to end into adjacent convolutions to provide acontinuous helical corrugation, the corrugations 224 are separate andspaced from each other. The undulating configuration of the corrugatedportion 22!) also provides, in effect, radially outwardly extendingcorrugations 228 between adjacent corrugations 224, the corrugations 228being disposed in planes at right angles to the tube axis.

The crests 230 of the corrugations 228 are of the same outside diameterand are of the same diameter as the outside diameter of the cylindricalplain end portions of the inner tube. The crests 232 of the corrugations224 are of the same inside diameter and the tube 214 is of uniform wallthickness from one end to the other.

The tubes 212 and 214 are assembled together in any suitable manner sothat "a mechanical or metallurgical contact of the two tubes is achievedwith the crests 230 of the corrugations 228 contacting the smoothinternal surface of the outer tube. Preferably, the crests 230 have afull and continuous contact with the smooth internal surface of theouter tube. The external surfaces of the plane end portions of the tubealso have a full and continuous surface-to-surface contact with thesmooth internal surface of the outer tube.

It will be readily apparent that in the Figure 3 embodiment, the plaintube 12 might be substituted for the 4 finned tube 212, in which eventthe crests 230 and external surfaces of the ends of the inner tube wouldhave a full continuous and uninterrupted surface-to-surface contact withthe smooth inner surface of the outer tube 12.

The drawings and the foregoing specification constitute a description ofthe improved internal and internal-external surface heat exchangetubingin such full, clear, concise and exact terms as to enable anyperson skilled in the art to practice the invention, the scope of whichis indicated by the appended claim.

What I claim as my invention is:

A heat exchange tube assembly for use in a heat exchanger, said assemblycomprising an outer tube having smooth cylindrical radially inner andouter surfaces, and an inner tube telescope coaxially within said outertube in heat exchange relationship therewith, said inner tube being socorrugated as to have an undulating configurationin longitudinal sectionexcept at the ends thereof, the crests of the undulations being in fulland continuous surface-to-surface contact with the radially innersurface of said outer tube, the interior of said inner tube, from theaxis thereof radially outward, being in direct open communication withthe undulating inner surface of said inner tube and the undulationsbeing such that substantial turbulence is produced in fluid movingaxially through said inner tube, each of the opposite ends of said innertube having a smooth cylindrical radially outer surface which throughoutits entire circumference is in full and continuous surface-to-surfacecontact with the radially inner surface of said outer tube to isolatethe space between said tubes.

References Cited in the file of this patent UNITED STATES PATENTS1,005,441 Lovekin Oct. 10, 1911 1,564,446 Rhoads Dec. 8, 1925 1,818,082Mott Y Aug. 11, 1931 1,913,573 Turner June 13, 1933 2,118,060 Stone etal. May 24, 1938 2,271,131 Price Jan. 27, 1942 2,374,609 McCollum Apr.24, 1945 2,456,775 Fausek et al. Dec. 21, 1948 2,820,615 Peters Jan. 21,1958 FOREIGN PATENTS 684,602 Great Britain Dec. 24, 1952

